Cosmogenic 10Be and 36Cl ages from Late Pleistocene terminal moraine complexes in the Taylor River drainage basin, central Colorado, USA

Abstract

Cosmogenic surface-exposure ages from boulders on a terminal moraine complex establish the timing of the local last glacial maximum (LGM) in the Taylor River drainage basin, central Colorado. Five zero-erosion 10Be ages have a mean of 19.5±1.8ka while that for three 36Cl ages is 20.7±2.3ka. Corrections for modest rates (∼1mmka−1) of boulder surface erosion result in individual and mean ages that are generally within 2% of their zero-erosion values. Both the means and the range in ages of individual boulders are consistent with those reported for late Pleistocene moraines elsewhere in the southern and middle Rocky Mountains, and thus suggest local LGM glacier activity was regionally synchronous. Two anomalously young (?) zero-erosion 10Be ages (mean 14.4±0.8ka) from a second terminal moraine are tentatively attributed to the boulders having been melted out during a late phase of ice stagnation.